Hydrocephalus

Breeds Affected: Friesian

Samples Accepted: Blood, Hair

Disease Information: Hydrocephalus is an accumulation of fluid in the brain.  Pressure from the build-up of cerebrospinal fluid enlarges the skull of the foal.  This condition is lethal, and foals are often born early.  The large head size can also cause complications for the mare during foaling.

The possible genotypes are:

N/N The horse is normal, and cannot produce Hydrocephalus-affected offspring.

N/h The horse is a carrier of Hydrocephalus, and can pass the allele on to approximately 50% of any offspring. If bred to another N/h carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.

h/h The horse is affected with Hydrocephalus.  This condition is fatal.

 Recommendations:
– Carriers may be bred to normal animals (N/h x N/N) without any risk of producing affected offspring. The offspring should also be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/h x N/h) is not recommended due to the possibility of 25% of the offspring being affected.

Inheritance Information: Animals which have two copies of this allele are affected with Hydrocephalus, and animals with one copy are clinically-normal carriers.

Test Information: This mutation test identifies a single base pair change in exon 12 of the B3GALNT2 gene.

Ducro, B.J., Schurink, A., Bastiaansen, J.W., Boegheim, I.J., van Steenbeek, F.G., Vos-Loohuis, M., Nijman, I.J., Monroe, G.R., Hellinga, I., Dibbits, B.W., Back, W., Leegwater, P.A.: A nonsense mutation in B3GALNT2 is concordant with hydrocephalus in Friesian horses. BMC Genomics 16:761, 2015. Pubmed reference: 26452345. DOI: 10.1186/s12864-015-1936-z.

Further information is available at the Online Mendelian Inheritance in Animals website.